:orphan:
.. _mmf_X2C:
Molecular mean-field X2C
========================
The molecular-mean-field X2C Hamiltonian (X2Cmmf) is **available** for the following methods:
- Coupled Cluster (CC): module RELCCSD
- multi-reference (MR) CC: Fock-space CC (including the intermediate Hamiltonian IHFSCC version): module RELCCSD
The remaining post-SCF modules are **not supported** yet:
- KR-MCSCF
- KR-CI
- TD-DFT
The X2Cmmf Hamiltonian scheme can be used for the Dirac-Coulomb as well
as the Dirac-Coulomb-Gaunt Hamiltonian (add .GAUNT to \*\*HAMILTONIAN).
One-step X2Cmmf
---------------
In order to perform a two-component (MR)CC after a four-component SCF calculation add the keyword .X2Cmmf
to the \*\*HAMILTONIAN keyword section:
::
**HAMILTONIAN
.X2Cmmf
After the SCF calculation Dirac will carry out the transformation to two-component prior to the 4-index transformation of
the two-electron integrals and the CC run.
Two-step X2Cmmf
---------------
Besides the one-step X2Cmmf protocol as described above one may also proceed in seperate steps.
This may be useful if one would like to use less/more MPI processes in the SCF+decoupling step than in the 4-index/CC calculation.
The first step (SCF+decoupling) simply requires the .X2Cmmf keyword under the \*\*HAMILTONIAN input deck (same as above):
::
**HAMILTONIAN
.X2Cmmf
Save the files DFCOEF, AOMOMAT and X2CMAT, for example using the *pam* script::
./pam ... --outcmo --get="AOMOMAT X2CMAT"
To restart now any further calculation, for example the 4-index transformation (MOLTRA) and/or the (MR)CC run copy the above files to
your scratch directory::
./pam ... --incmo --put="AOMOMAT X2CMAT"
and set the keyword combination as indicated below under the \*\*HAMILTONIAN input deck::
**HAMILTONIAN
.X2C
*X2C
.mmf-restart
In order to run a (MR)CC calculation add also the following keyword(s) to the namelist RELCCSSD input::
*CCSORT
.USEOE
.NORECMP
END
or the new RELCCSD deck input::
*CCSORT
.NORECMP
Dirac will automatically read the two-component coefficients from the file DFCOEF and proceed in two-component mode for
any wave function analysis or post-HF step required for a (MR)CC calculation.